As a method of forming a conductive layer of an n type or a p type at a semiconductor wafer, there is used a so-called ion implantation technology of accelerating a conductive type dopant ionized by an ion source by an electric field to implant to a wafer. According to the ion implantation technology, a plasma is generated by ionizing a gas supplied to an ion source in a plasma chamber, and an ion beam is extracted from the plasma by applying a predetermined voltage to an extracting electrode. Successively, an ion beam comprising an ion having a desired mass is extracted by making the extracted ion beam incident on a mass analysis magnet apparatus, the ion beam is made to pass through a mass analysis slit, thereafter, reciprocally scanned by a beam scanner and irradiated to a wafer to thereby carry out ion implantation (see Patent Reference 1: JP-A-2006-156259).
In such an ion implantation technology, there is provided an injector flag Faraday cup having a function of shutting off an ion beam as necessary and measuring a total beam current to be able to be brought in and out to and from a beam line. Graphite is provided at a portion of the injector flag Faraday cup on which an ion beam impinges, and when the injector flag Faraday cup is inserted into the beam line, the ion beam is shut off by making the ion beam impinge on the graphite.
Specifically, as shown by FIG. 1A and FIG. 1B, an injector flag Faraday cup 200 is provided at inside of a scanner housing 310 along with a beam scanner 300. As explained later, the beam scanner 300 is for periodically reciprocating an incident ion beam in a horizontal direction orthogonal to an advancing direction thereof by a pair of scanning electrodes 300-1 and 300-2 arranged to be opposed to each other to interpose a beam trajectory line. An upstream side and a downstream side of the beam scanner 300 are respectively provided with scanner suppression electrodes 320 and 330 for restraining diversion of the ion beam and restricting a section size of the ion beam. The injector flag Faraday cup 200 is arranged at a portion in correspondence with a downstream side adjacent to the scanner suppression electrodes 330.
The injector flag Faraday cup 200 is provided with a receiving area in correspondence with a range of scanning the ion beam by the beam scanner 300 and is made to be brought in and out to and from the beam line by a drive mechanism (not illustrated) installed at outside of the scanner housing 310, in this case, by being driven in an up and down direction. For example, during a time period until interchanging a wafer finished with ion implantation by a wafer which has not been implanted yet, the injector flag Faraday cup 200 is placed at the beam line to shut off the ion beam. A portion of the injector flag Faraday cup 200 on which the ion beam impinges is covered by a material of graphite or the like which is strong at sputtering by the ion beam.